A coroner says a fatal South Canterbury crash highlights the dangers for diabetics driving during a low blood sugar episode.
Yvonne McGlashan, 59, died after her car crossed the centre line and crashed into a truck and trailer unit on State Highway 1 near Orari, about 30km north of Timaru.
Evidence indicated that Ms McGlashan, a diabetic for more than 40 years, had been driving erratically earlier after leaving Timaru on November 18, 2010 intending to visit her daughter in Christchurch.
She was weaving in her lane and speeding up and slowing down, and another driver ahead of her slowed down in an attempt to slow Ms McGlashan down in Winchester, about 15 minutes before the fatal crash.
He described Ms McGlashan as looking "vacant".
Her husband John McGlashan said she knew her symptoms well and usually ate if she could feel a low blood sugar episode, or hypoglycaemia, coming on.
He said she was especially diligent after crashing into a fence about six years earlier, and she appeared normal when he went to work four hours before she started driving.
Coroner Richard McElrea said the evidence overwhelmingly suggested Ms McGlashan was hypoglycaemic at the time of the crash but failed to recognise it as it happened after she started driving.
"The facts of this case and the expert opinion given highlight that hypoglycaemia may not only impair driving safety but also judgment as to whether to continue to drive or self-treat."